This invention relates generally to the construction of vehicle tires and relates, more particularly, to a transfer ring used in a tire construction process.
During the construction of a vehicle tire, a tire carcass is built upon a first stage tire-building drum and transferred to a second stage drum (e.g. a shaping drum) where it awaits a belt and tread package of the vehicle tire to be positioned thereon. The belt and tread package is constructed on a separate drum (i.e. a belt and tread drum) and transferred, by way of a transfer ring, to the second stage drum upon which the carcass has already been positioned. While positioned about a belt and tread drum, the belt and tread package is encircled and grasped by the transfer ring, and the belt and tread drum is collapsed so that the belt and tread package is supported by the transfer ring for subsequent transfer to the second stage drum.
With the belt and tread package supported within the transfer ring, the package is placed around the tire carcass disposed about the second stage drum, and the tire carcass is subsequently inflated in a manner which urges the outer surface of the tire carcass against the interior of the belt and tread package to form a tire precursor which is later placed in a mold for final formation of the tire and its tread.
A transfer ring commonly includes a pair of stationary outer ring-shaped housing rings, an actuator ring disposed between the housing rings and a plurality of tire-grasping shoes which are positioned about so as to collectively define a substantially circular spacing between the shoes, and it is this circular spacing that accepts a belt and tread package when the transfer ring is moved over the package. Each of the shoes has a radially inwardly-facing surface which is movable radially inwardly and outwardly with respect to the circular spacing defined thereby for movement into and out of engagement with the outer circumference, or peripheral surface, of the belt and tread package. The shoes are supported by the outer housing rings and the actuator ring by way of a linkage system so that appropriate movement of the linkage system (by way of, for example, an air-actuated cylinder) effects the simultaneous movement of all of the shoes into or out of engagement with the outer circumference of the belt and tread package. An example of a transfer ring of the aforedescribed class and which is capable of grasping a belt and tread package for transference of the package to a position about a tire carcass is described in U.S. Pat. No. 5,441,587.
After positioning the transfer ring about a belt and tread package and moving its shoes into engagement with the belt and tread package, it is desirable that the package remains firmly grasped by the shoes as the package is transferred into position about a tire carcass positioned about the second stage drum. However, in some instances, the size (e.g. the diameter) of the package tends to contract due, for example, to hoop stress which may be induced within the package when constructed, and unless compensated for, such a contraction of the package size could relieve some of the grasping pressure being applied to the package by the shoes so that the package is permitted to deform to a deleterious shape.
After the belt and tread package has been transferred to a position about the carcass, the carcass is inflated against the interior surface of the belt and tread package to help join the carcass to the belt and tread package. In order that the rounded shape of the outer surface of the belt and tread package is maintained during the carcass-inflating process, the package continues to be grasped by the shoes as the carcass is inflated. However, radially outwardly-directed forces which are exerted against the shoes during the inflation of the carcass can be so great that the shoes tend to be displaced radially outwardly from their original position of engagement with the outer circumference of the belt and tread package. Such a radially outwardly-directed displacement, or shifting, of the shoes due to such outwardly-directed forces (referred to herein as backdriving forces) is a highly undesirable occurrence in that it promotes inaccuracies in the dimensions of the tire being constructed (i.e. permits the enlargement of the belt and tread package beyond a desired diameter) and can promote damage to various components of the transfer ring which oppose the backdriving forces.
It would therefore be desirable to provide a transfer ring having an improved means for resisting backdriving forces generated during a tire carcass-inflating operation which tend to urge the package grasping-shoes radially outwardly of the position assumed by the shoes when initially placed into grasping relationship with the belt and tread package yet accommodates, if necessary, a contraction of the belt and tread package between the moment that the package is initially grasped by the shoes and the carcass-inflating step while the shoes maintain a substantially uniform grasping pressure about the belt and tread package.
Accordingly, it is an object of the present invention to provide a new and improved transfer ring of the aforedescribed class which both resists backdriving forces generated during a tire carcass-inflating operation so that the shoes which are grasped about the belt and tread package are not shifted radially outwardly of the position assumed by the shoes when initially placed into grasping relationship with a belt and tread package and accommodates a contraction of the belt and tread package after the package has been initially grasped by the shoes.
Another object of the present invention is to provide such a transfer ring which positively limits any radially outwardly-directed expansion of the belt and tread package during a carcass-inflating operation to the diameter possessed by the belt and tread package when initially grasped by the package-grasping shoes to promote dimensional accuracy within the tire being constructed.
Yet another object of the present invention is to provide such a transfer ring which utilizes a novel braking scheme for preventing undesired backdriving of the package-grasping shoes during a carcass-inflating process.
Still another object of the present invention is to provide such a transfer ring whose package-engaging shoes apply an amount of radially inwardly-directed biasing force upon the belt and tread package when placed in desired grasping relationship with the package to maintain a substantially uniform grasping pressure about the package even if the package were to contract in size after the package has been initially grasped by the shoes.
Yet another object of the present invention is to provide such a transfer ring having an improved means for joining the shoes of the transfer ring to one another to help ensure that the shoes act in unison during use of the transfer ring.
A further object of the present invention is to provide such a transfer ring which is uncomplicated in structure, yet effective in operation.